A CATV system using a communication satellite or a broadcasting satellite is consisted of a broadcasting station, the satellite, a local CATV center, and a plurality of terminal devices of subscribers.
The television (TV) signal from the broadcasting station to the local CATV center through the satellite is scrambled with a high level encoding. In order to descramble the highly scrambled TV signal, an expensive decoder is necessary. Such an expensive decoder is not suitable for subscribers. Therefore, the local center descrambles the TV signal and re-scrambles it with a low level encoding suitable for the subscribers. However, if the TV signal for the commercial program is scrambled, non-subscribers cannot watch the commercial program. Therefore, the broadcasting station must transmit the TV signal for the commercial program without scrambling, and the local CATV center must not scramble the TV signal.